Resonant charge pump circuit with synchronized switching

ABSTRACT

A resonant charge pump circuit includes a resonant circuit having a bucket capacitor and a bucket inductor connected in series, and a switching circuit connected to the resonant circuit. The switching circuit switches to a first state that enables current to flow from an input terminal into the resonant circuit to charge the bucket capacitor and the bucket inductor, and switches to a second state that enables current to flow from the resonant circuit to discharge the bucket capacitor and the bucket inductor to an output terminal. The resonant circuit controls current flow into and out from the resonant circuit when the switching circuit switches between the states. The resonant charge pump circuit also includes a timing circuit that controls when the switching circuit switches between the states.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119 of U.S.Provisional Application No. 62/786,238, filed on Dec. 28, 2018, andentitled “Resonant Charge Pump Circuit,” which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

The present invention relates generally to charge pumps, and inparticular, to a high-power and high-efficiency resonant charge pump.

BACKGROUND INFORMATION

A very common requirement in electronic circuits is to convert anavailable DC voltage source to a lower or higher DC voltage. One way todo this is by using a charge pump circuit. The charge pump uses acapacitor as an energy-storage element. During operation, current(charge) is alternately switched and directed between two capacitorsarranged so that the circuit output is twice the input, and thusfunctioning as a voltage-doubling boost converter. In otherconfigurations, the charge pump acts as a voltage “divider” in half orstep-down converter.

Unfortunately, a traditional charge pump circuit may not be suitable forhigh power applications, even though it is known to have fairly goodconversion efficiency. For example, during the charge pump's switchingoperation, a large amount of current flows through the components in avery short time period. This is referred to as inrush current and hasthe potential to damage circuit elements (e.g., fusing devices orplacing high stress on devices).

Therefore, it is desirable to have a high-efficiency charge pump circuitthat is suitable for high power applications and that overcomes theproblems associated with conventional circuits.

SUMMARY

In various embodiments a high-power and high-efficiency resonant chargepump circuit is provided. The resonant charge pump overcomes theproblems associated with large inrush currents experienced byconventional circuits. Therefore, embodiments of the resonant chargepump are suitable for applications where high-power and high-efficiencyare desired. As an added benefit, the resonant charge pump operates withvery low electromagnetic interference (EMI).

In one embodiment, a resonant charge pump circuit is provided thatincludes a resonant circuit having a bucket capacitor and a bucketinductor connected in series, and a switching circuit connected to theresonant circuit. The switching circuit switches to a first state thatenables current to flow from an input terminal into the resonant circuitto charge the bucket capacitor and the bucket inductor, and switches toa second state that enables current to flow from the resonant circuit todischarge the bucket capacitor and the bucket inductor to an outputterminal. The resonant charge pump circuit also includes a firstswitching element between the input terminal and the resonant circuitand a second switching element between the resonant circuit and theoutput terminal, and a timing circuit that controls when the switchingcircuit switches between the states.

In another embodiment, an integrated circuit is provided that includes aclock generator that generates single or multiple of clock signals todrive an external resonant circuit to control switch-mode powerconversion. The integrated circuit also includes means for detectingphase timing of the resonant circuit such that the clock generatorsynchronizes the clock signals to the phase timing of the resonantcircuit.

Further details and embodiments are described in the detaileddescription below. This summary does not purport to define theinvention. The invention is defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, where like numerals indicate like components,illustrate embodiments of the invention.

FIG. 1A shows an embodiment of a charge pump circuit.

FIG. 1B shows an embodiment of a charge pump circuit.

FIG. 2A show diagrams that illustrate current flow through the chargepump circuit shown in FIG. 1A.

FIG. 2B shows an alternate embodiment of the charge pump circuit shownin FIG. 1A that reduces inrush currents.

FIG. 2C shows diagrams that illustrate the operation of the charge pumpcircuit shown in FIG. 1A with the addition of the resistor R₀.

FIG. 3A shows an embodiment of a resonant charge pump circuit.

FIG. 3B shows an embodiment of a resonant charge pump circuit.

FIG. 4 shows an embodiment of a resonant charge pump circuit thatsimulates the operation of a resonant charge pump circuit shown in FIG.3.

FIG. 5 shows graphs that illustrate voltage and current waveformsassociated with synchronized operation of the resonant charge pumpcircuit shown in FIG. 4.

FIG. 6 shows graphs that illustrate voltage and current waveformsassociated with unsynchronized operation of the resonant charge pumpcircuit shown in FIG. 4.

FIG. 7 shows an embodiment of a resonant charge pump circuit thatincludes a synchronization circuit.

FIG. 8 shows an embodiment of a resonant charge pump circuit withsynchronization.

FIG. 9 shows graphs that illustrate voltage and current waveformsassociated with the resonant charge pump circuit shown in FIG. 8.

DETAILED DESCRIPTION

Reference will now be made in detail to some exemplary embodiments ofthe invention, examples of which are illustrated in the accompanyingdrawings.

FIG. 1A shows an embodiment of a charge pump circuit 100. The chargepump circuit 100 converts a low voltage (V_(LOW)) to a higher voltage(V_(HIGH)) where V_(HIGH)=V_(LOW)×2. A buffer (BUF1) receives a clocksignal that causes the buffer output to switch between a first level atV_(LOW) and a second level at ground. When the BUF1 output is at ground,a current (i_(BKT)) flows into a bucket capacitor (C_(BKT)) and chargesthe bucket capacitor up to the level of V_(LOW). When the output of theBUF1 switches to the V_(LOW) level, the voltage of the bucket capacitoris added to the BUF1 output such that the voltage level at the output ofdiode D2 is equal to (2×V_(LOW)). Thus, the charge pump circuit 100 actsas a voltage doubler.

FIG. 1B shows an embodiment of a charge pump circuit 102. The circuit102 converts the voltage V_(HIGH) to a lower voltage (V_(LOW)) whereV_(LOW)=V_(HIGH)/2. The circuit 102 performs in a similar manner to thecircuit 100 but operates to reduce the input voltage V_(HIGH) to theoutput voltage (V_(LOW)). Thus, the circuit 102 acts as a voltagedivider or step-down charge pump. The two circuits (100 and 102) aresymmetrical and have similar disadvantages when used in high powerapplications. For example, the two circuits experience large inrushcurrents when the buffer switches state. These large inrush current candamage circuit components. This issue is illustrated in greater detailbelow.

FIG. 2A show diagrams 200 that illustrate current flow through thecharge pump circuit 100 shown in FIG. 1A. The diagrams 200 show theclock signal and the bucket current i_(BKT). As can be seen from thediagrams 200, when the clock signal switches state, the bucket currenti_(BKT) experiences a large current spike. These current spikes havevery large amplitude (I₀) and occur over a very short time duration(T₀). In high power applications, these current spikes can become verylarge. If this charge pump circuit is used in high power applications,an additional circuit would be needed to avoid the huge inrush currents,otherwise the inrush currents could damage circuit elements (fusingdevices or placing high stress on devices) that may shorten productlife. Thus, it is desirable to have a way to control or reduce theinrush current spikes.

FIG. 2B shows an alternate embodiment of the charge pump circuit 100shown in FIG. 1A that reduces inrush currents. For example, a resistoris added to the charge pump circuit 100 shown in FIG. 1A to control orreduce inrush current spikes. For example, the circuit 202 illustrateshow a resistor (R₀) is added to the output of BUF1. The resistor R₀reduces the inrush current since the inrush current through R₀ generatesa voltage drop that reduces the voltage across C_(BKT). However, use ofthe resistor (R₀) also reduces conversion efficiency.

FIG. 2C shows diagrams 204 that illustrate the operation of the circuit100 with the addition of the resistor R₀. The diagrams 204 show theclock signal and the bucket current i_(BKT). As can be seen from thediagrams 204, when the clock signal switches state, the bucket currenti_(BKT) experiences a reduced current spike. For example, the currentspikes have amplitude (I₁) that is smaller than (I₀) and less likely todamage circuit components. These smaller spikes occur over a timeduration (T₀) that has a time-constant based on R₀ and C_(BKT), which islonger than (T₀). Thus, with the addition of the resistor R₀, it ispossible to use the charge pump circuits shown in FIG. 1A in highvoltage applications. However, it should be noted that the resistor R₀also reduces conversion efficiency of the charge pump circuit.Therefore, it is desirable to have a way to control or reduce currentspikes without affecting the efficiency of the charge pump circuit.

Resonant Charge Pump Circuit

FIG. 3A shows an embodiment of a resonant charge pump circuit 300. Theresonant charge pump circuit 300 converts a low voltage (V_(LOW)) to ahigher voltage (V_(HIGH)) where V_(HIGH)=V_(LOW)×2. The resonant chargepump circuit 300 is similar to the charge pump circuit 100 shown in FIG.1A except that an inductor (or coil) L_(BKT) 302 has been added at theoutput of BUF1. The inductor L_(BKT) 302 combines with the capacitorC_(BKT) to form a resonant circuit that operates to control or reducethe current spikes. In exemplary embodiments, an LC resonant circuitproduces current flow that is sinusoidal in shape, and therefore theinrush current problem is solved. Since the resonant circuit has noresistance or power loss, it is suitable to control or reduce thecurrent spikes in charge pump circuits even in high power applications.

FIG. 3B shows an embodiment of a resonant charge pump circuit 304. Thecircuit 304 converts the voltage V_(HIGH) to a lower voltage (V_(LOW))where V_(LOW)=V_(HIGH)/2. The circuit 304 is similar to the charge pumpcircuit 102 shown in FIG. 1B except that an inductor (or coil) L_(BKT)306 has been added at the output of BUF2. It should be noted thatalthough the inductor 306 is located on the opposite side of C_(BKT),the effects of the resonant circuit are the same as in the resonantcharge pump circuit 300.

FIG. 4 shows an embodiment of a resonant charge pump circuit 400 thatsimulates the operation of the resonant charge pump circuit 300 shown inFIG. 3. With the goal of high power applications in mind, the circuit400 includes transistors SW3 and SW4 that replace diodes D1 and D2. Thecircuit 400 also includes a switching circuit 410 that comprises buffer416, transistors switches SW1, SW2 and resistors R1, R2. The circuit 400also includes output load capacitor CL and resistor RL.

The transistors SW3 and SW4 are synchronized to a control clock signal412. The circuit 400 also includes bucket capacitor (C_(BKT)) 406 andbucket inductor (L_(BKT)) 408 that form an LC resonant circuit 414 thatmaintains its self-oscillation for a long time period (ideally, foreveroscillation) until parasitic resistance converts resonant energy intoheat. The switching circuit 410 functions as BUF1 to receive the clocksignal 412 and generate an output (SW) that switches state betweenV_(low) and ground in response to the clock signal 412.

The self-resonant LC circuit 414 delivers the energy back and forth tothe node VM. To maintain the direction of energy delivery, the timing ofthe switching needs to be synchronized to the LC resonant frequency. Asa result, the circuit 400 receives a low input voltage (Vin) (e.g., 12volts) and generates a high output voltage (Vout) that is approximatelytwice the input voltage (2×Vin). The operations of the resonant chargepump circuit 400, both synchronized and unsynchronized, are shown inFIGS. 5-6, respectively.

FIG. 5 shows graphs 500 that illustrate voltage and current waveformsassociated with synchronized operation of the resonant charge pumpcircuit 400 shown in FIG. 4. For example, graphs 500 include graph 502showing i_(BKT) current, graph 504 showing input current (iin), graph506 showing voltage across C_(BKT) 406, and graph 508 showing outputvoltage (Vout). As illustrated in the graph 502, the resonant circuit(C_(BKT), L_(BKT)) has eliminated large current spikes on the i_(BKT)current. For example, the graph 502 shows a perfectly sinusoidal i_(BKT)current waveform. Thus, the resonant circuit suppresses current spikeswhen BUF1 (switching circuit) switches between the first and secondstates. It should be noted also that the graph 508 of the output voltageshows that the output voltage (e.g., 24 volts) remains constant at(2×V_(LOW)). These results show that the synchronized resonant circuitreduces or eliminates large inrush current thereby allowing the resonantcharge pump circuit to be used in high power applications.

FIG. 6 shows graphs 600 that illustrate voltage and current waveformsassociated with unsynchronized operation of the resonant charge pumpcircuit 400 shown in FIG. 4. For example, graphs 600 include graph 602showing i_(BKT) current, graph 604 showing input current (iin), graph606 showing voltage across C_(BKT) 406, and graph 608 showing outputvoltage (Vout). As can be seen from the graph 608, the output “dashedline” 610 is below 20V (and not 24 volts) because of the unsynchronizedenergy delivery of the LC circuit. Thus, it is desirable to have a wayto maintain synchronization of the resonant charge pump circuit toobtain proper operation as illustrated in FIG. 5.

Resonant Charge Pump Synchronization

FIG. 7 shows an embodiment of a resonant charge pump circuit 700 thatincludes a synchronization circuit 714. In one embodiment, a currentsensor 712 senses current on the BUF1 output. The sensed current isinput to a zero-current detector 702 that detects zero-current events onthe BUF1 output. Detection pulses associated with the detectedzero-current events are input to an “OR” device 706 that also receives aclock signal from an alternate clock generator 704 (discussed in greaterdetail below). During normal operation, the detection pulses output fromthe detector 702 flow through the OR device 706 and are input to atoggle flip flop (FF) 708. The output of the FF 708 is used to generatecomplementary synchronized clock signals S1 and S2 that drive theswitches (SW 1-4) of the resonant charge pump circuit 700. In anothermode of operation, if the detector 702 fails to detect zero-currentevents, the alternate clock generator 704 generates an alternate clock716 that passes through the OR device 706 to the input of the toggle FF708. Thus, in the case of low current through the LC circuit, such thatno zero-current events are detected, the alternate clock generator 704generates the clock signals used by the resonant charge pump circuit. Inone embodiment, the synchronization circuit 714 is implemented on anintegrated circuit.

During operation of the resonant charge pump circuit 700, the directionof energy delivery is maintained by detecting the zero-current flowtiming of the LC resonant circuit 718. In one embodiment, whenzero-current events of the LC resonant circuit 718 are detected,synchronized control clocks (S1, S2) change state from high-to-low orlow-to-high. Appropriately changing the state of the control clocksresults in current flow in one direction.

Alternate Clock Generator

When a load of the resonant charge pump circuit 700 becomes very small,it may become difficult for the zero-current detector 702 to detect“zero current” events because current delivered by the LC resonantcircuit 718 may fall below the detection threshold. In this case, thealternate clock generator 704 operates to keep the circuit pumping. Inone embodiment, a simple logic timing circuit can be used to generatethe alternate clock 716. When no detection pulses are output from thezero-current detector 702, the alternate clock generator 704 start itstimer and maintains periodic S1/S2 flipping. In this condition, the loadcurrent is very small, it is of little effect if the alternate clocktiming is synchronized or not. It is preferable to set this alternateclock period almost equal to or slightly longer than the LC resonantdesign target.

In various embodiments, the “zero-current sense” circuit may have acertain limit on its detection range. This is a case of light to zeroload current from the output side (either one of V_(LOW) or V_(HIGH))depending on step-down or step-up pumping operation.

In a light-load condition, because of almost negligible current flowbetween the input and output sides, maintaining accurate LC resonantfrequency timing on the control clock signals S1 and S2 is not required.It is desirable to supply approximate timing on the clock signals S1 andS2 to maintain the output voltage. Thus, the alternate clock generator704 maintains clocking of the S1 and S2 signals while the zero-currentsensing circuit is out of operation (sensing).

FIG. 8 shows an embodiment of a resonant charge pump circuit 800 withsynchronization. In one embodiment, the circuit 800 is an implementationof the circuit 700 shown in FIG. 7. The circuit 800 includes thezero-current detector 702, alternate clock generator 704, and toggle FF708. The results of the operation of the resonant charge pump circuit800 are shown in FIG. 9. In one embodiment, the zero-current detector702, alternate clock generator 704, and toggle FF 708 are implemented onan integrated circuit.

As discussed above, if there is very small current into the LC circuit,the zero-current detector 702 may not detect zero current eventsproperly. In one embodiment, two diodes (802, 804) are inserted acrossthe transistors (SW3, SW4) that function as diodes D1 and D2 shown inFIG. 1A. In one embodiment, it may be preferable to stop usingtransistors SW3 and SW4 when the alternate clock 716 is driving the S1and S2 signals. The diodes (802, 804) maintain the output voltage duringthis time. Since this is a light-load condition, there is no need toworry about power loss. The diodes (802, 804) can suppress unneeded LCresonant ringing during the light-load condition. In one embodiment, thediodes (802, 804) are body diodes that are part of FET transistors usedas SW3 and SW4.

As illustrated in FIG. 8, the zero-current detector 702 comprises asense resistor (Rs), comparator 806, a rising edge triggered one shot808, a negative edge triggered one shot 810 and an OR gate 812. Duringoperation, zero current events are detected as changing voltage acrossthe sense resistor Rs that are input to the comparator 806. Thecomparator 806 responds by outputting either a rising edge or fallingedge signal that triggers one of the one shots 808, 810 to output apulse to the OR gate 812. The OR gate 812 passes this pulse as a triggerpulse 822 to the alternate clock generator 704.

As illustrated in FIG. 8, the alternate clock generator 704 comprises atimer circuit 816, one-shot circuit 818, and OR gate 814. The timingperiod 826 of the timer circuit 816 is set to be longer than theexpected LC resonant frequency (including coil and capacitor tolerance).As long as the zero-current detector 702 outputs a trigger pulse 822when there is a current flow direction change (e.g., zero-currentsensing), the timer 816 will be reset and the timing of the clocksignals S1 and S2 remains under the control of the zero-current sensecircuit 702.

When in a light-load condition, the zero-current detector 702 fails todetect zero-current events and stops sending trigger pulses 822. At thispoint, the timer 816 is allowed to complete its timing cycle (timer runsout) and initiates a trigger pulse from the one-shot 818. The output ofthe one shot 818 form the alternative clock 716 that flows through theOR gate 814 to toggle the flip-flop 820 and the clocks S1 and S2 tomaintain the charge pump output. The pulse output of OR gate 814 alsorestarts the timer 816 so that the cycle of clocking S1 and S2 isrepeated. Since the time period 826 provided by the timer 816 is set tobe longer than the main LC resonant timing, as soon as the resonantcharge pump circuit gets out from the light-load condition, thezero-current sensing circuit 702 takes over control of the timing of theS1 and S2 signals.

FIG. 9 shows graphs 900 that illustrate voltage and current waveformsassociated with the resonant charge pump circuit shown in FIG. 8. Forexample, the graphs 900 include graph 902 that shows the alternate clock716, graph 904 that shows i_(BKT) current, graph 906 that shows inputcurrent fin, graph 908 that shows voltage across the bucket capacitor(C_(BKT)), and graph 910 that shows the output voltage (Vout) of theresonant charge pump.

As illustrated in graph 902, the alternate clock 716 provides clockpulse signals when the load current is small, for example, as indicatedby the input current shown in graph 906. When the load current increasesand zero-current events begin to occur (shown at time indicator 912) thezero-current detector 702 and the LC resonant circuit take over togenerate synchronized clock signals. This can be seen by the cleansinusoid waveforms after the time indicator 912, which result from thezero-current events that are detected by the zero-current detector 702.It should be noted that regardless of whether the synchronized clocksgenerated by the zero-current detector 702 or alternate clocks generatedby the alternate clock generator 704 are utilized, the resonant chargepump circuit continues to output a stable 24-volt output as illustratedin graph 910.

Low EMI Circuit Operation

In various embodiments, the resonant charge pump circuit operates withvery low noise. For example, during low load current conditions, theresonant charge pump is not synchronized and operates based on thealternate clock. Since the energy that flows is so low, the circuitemits low EMI. During synchronous operation of the resonant charge pumpcircuit, the circuit operates using zero-current-switching (ZCS). Thisoperating mode is well known to provide very good noise performancebecause high power transistors are switching when no current is flowing.Generally, EMI noise power comes from sudden changes of current flow,but the resonant charge pump circuit utilizes ZCS, which results in lowEMI.

Although certain specific embodiments are described above forinstructional purposes, the teachings of this patent document havegeneral applicability and are not limited to the specific embodimentsdescribed above. The function of the hardware circuitry illustrated inthe figures can be implemented in hardware circuitry as shown, or in acombination of dedicated hardware circuitry and software, or largely insoftware. Accordingly, various modifications, adaptations, andcombinations of various features of the described embodiments can bepracticed without departing from the scope of the invention as set forthin the claims.

What is claimed is:
 1. A resonant charge pump circuit, comprising: afirst switching element connected to a second switching element at afirst node, the first and the second switching elements connected inseries between an input terminal and an output terminal; a resonantcircuit connected between the first node and a second node, the resonantcircuit having a bucket capacitor and a bucket inductor connected inseries; and a synchronization circuit connected to the second node andoperable to output a first control signal and a second control signal,the synchronization circuit comprising an alternate clock generator thatis operable to cause the first and the second control signals to beoutput when a predetermined current level is not detected at the secondnode, wherein: the first and the second control signals are synchronizedand complementary; the first control signal is operable to control astate of the first switching element; and the second control signal isoperable to control a state of the second switching element.
 2. Theresonant charge pump circuit of claim 1, further comprising: a firstdiode connected between the input terminal and the first node; and asecond diode connected between the first node and the output terminal.3. The resonant charge pump circuit of claim 1, wherein: the firstcontrol signal is operable to cause the first switching element toconnect the input terminal to the resonant circuit when the firstswitching element is in a first state and cause the first switchingelement to disconnect the input terminal from the resonant circuit whenthe first switching element is in a second state; and the second controlsignal is operable to cause the second switching element to connect theresonant circuit to the output terminal when the second switchingelement is in the second state and to cause the second switching elementto disconnect the output terminal from the resonant circuit when thesecond switching element is in the first state.
 4. The resonant chargepump circuit of claim 3, wherein the first and the second switchingelements comprise transistors.
 5. The resonant charge pump circuit ofclaim 1, wherein the synchronization circuit synchronizes the switchingof the first and the second switching elements to a resonant frequencyof the resonant circuit.
 6. The resonant charge pump circuit of claim 1,wherein: the synchronization circuit comprises a current sensorconnected to the second node and a detector circuit connected to thecurrent sensor; and the detector circuit is operable to detect a currentlevel through the resonant circuit and cause the first and the secondcontrol signals to be output when the predetermined current level isdetected.
 7. The resonant charge pump circuit of claim 6, wherein: thedetector circuit is connected to an OR device; the alternate clockgenerator is connected to the OR device, the alternate clock generatoroperable to output an alternate clock signal; and the alternate clocksignal is operable to cause the first and the second control signals tobe output when the predetermined current level is not detected.
 8. Theresonant charge pump circuit of claim 7, wherein the predeterminedcurrent level is zero current.
 9. The resonant charge pump circuit ofclaim 7, wherein the synchronization circuit comprises: a toggle circuitconnected to the OR device, the toggle circuit operable to output thefirst control signal; and an inverter connected to the toggle circuit,the inverter operable to output the second control signal; and theswitching between the first and second states is controlled so thatcurrent spikes are reduced.
 10. The resonant charge pump circuit ofclaim 1, comprising: a third switching element; and a fourth switchingelement connected to the third switching element at a third node, thethird and the fourth switching elements connected in series between thesecond node and a fourth node, wherein the first switching element isconnected between the first node and the fourth node.
 11. A method foroperating a resonant charge pump circuit having a resonant circuit thatincludes a bucket capacitor and a bucket inductor, the methodcomprising: switching to a first state that enables current to flow froman input terminal into the resonant circuit to charge the bucketcapacitor and the bucket inductor; switching to a second state thatenables current to flow from the resonant circuit to discharge thebucket capacitor and the bucket inductor to an output terminal;synchronizing the switching between the first and second states by usinga signal output from a detector circuit to cause a first control signaland a second control signal to be output to control the current flowsfrom the input terminal to the output terminal; determining a currentlevel through the resonant circuit; and based on a determination thatthe current level is greater than a predetermined current level,synchronizing the switching between the first and second states by usingan alternate clock signal output from an alternate clock generator tocause the first control signal and the second control signal to beoutput to control the current flows from the input terminal to theoutput terminal, wherein: the first and the second control signals aresynchronized and complementary; the first control signal controls theswitching to the first state; and the second control signal controls theswitching to the second state.
 12. The method of claim 11, furthercomprising: connecting the input terminal to the resonant circuit usinga first diode; and connecting the resonant circuit to the outputterminal using a second diode.
 13. The method of claim 11, furthercomprising: connecting the input terminal to the resonant circuit whenin the first state and disconnecting the input terminal from theresonant circuit when in the second state; and connecting the resonantcircuit to the output terminal when in the second state anddisconnecting the output terminal from the resonant circuit when in thefirst state.
 14. The method of claim 11, wherein the synchronizing ofthe switching between the first and second states by using the signaloutput from the detector circuit comprises synchronizing the switchingbetween the first and second states to a resonant frequency of theresonant circuit.
 15. The method of claim 11, wherein the synchronizingof the switching between the first and second states by using the signaloutput from the detector circuit comprises generating the first and thesecond control signals using the signal output from the detector circuitto control the switching when the predetermined current level isdetected.
 16. The method of claim 15, wherein the predetermined currentlevel is zero current.
 17. The method of claim 11, wherein thesynchronizing of the switching between the first and second states byusing the signal output from the detector circuit controls the switchingbetween the first and the second states so that current spikes arereduced.
 18. A resonant charge pump circuit, comprising: a resonantcircuit; means for switching connected to the resonant circuit, whereinthe means for switching switches between a first state that enablescurrent to flow from an input terminal into the resonant circuit, and asecond state that enables current to flow from the resonant circuit toan output terminal; and means for synchronizing that uses a signaloutput from a detector circuit to cause a first control signal and asecond control signal to be output to control current flows from theinput terminal to the output terminal; means for determining a currentlevel through the resonant circuit; and based on a determination thatthe current level is greater than a predetermined current level, meansfor synchronizing the switching between the first and second states thatuses an alternate clock signal output from an alternate clock generatorto cause the first control signal and the second control signal to beoutput to control the current flows from the input terminal to theoutput terminal, wherein: the first and the second control signals aresynchronized and complementary; the first control signal controls theswitching to the first state; and the second control signal controls theswitching to the second state.
 19. The resonant charge pump circuit ofclaim 18, further comprising: a first switching element that connectsthe input terminal to the resonant circuit when the means for switchingis in the first state and disconnects the input terminal from theresonant circuit when the means for switching is in the second state;and a second switching element that connects the resonant circuit to theoutput terminal when the means for switching is in the second state anddisconnects the output terminal from the resonant circuit when the meansfor switching is in the first state.
 20. The resonant charge pumpcircuit of claim 18, wherein the means for synchronizing using thesignal output from the detector circuit synchronizes the means forswitching to switch between the first state and the second state at aresonant frequency of the resonant circuit.